1. Field of the Invention
This invention is related to a pumping assembly for pumping a viscous resin or similar fluid from a storage container to a mixing head or zone where the resin will be mixed with a reactive catalyst in a suitable reactive ratio. This invention is also related to the use of rotary lobe pumps to transport viscous fluids.
2. Description of the Prior Art
Rotary lobe pumps are commonly employed in the food and food processing industries, because they are capable of transferring viscous materials. Rotary lobe pumps have also been employed in oil delivery systems in high performance automotive and racing applications. In principle, a lobe pump is similar to an external gear pump. Liquid flows into the region created as counter-rotating lobe rotors unmesh. Displacement volumes are formed between the surfaces of each lobe rotor and the pump casing Liquid is displaced by the meshing of the lobe rotors, which are not mutually engaged and are spaced apart by distances on the order of 0.002 in. Relatively large displacement volumes enable nonabrasive solid suspended in a viscous fluid to be handled Liquid velocities and shear generally remain low making the rotary lobe pumps suitable for high viscosity, shear-sensitive liquids. Two, three and four lobe rotors have been used, depending upon solids size, liquid viscosity and tolerance of the system to flow pulsation. Two lobes generally handle larger solids and high viscosities, but the two lobe configurations tend to pulsate more. Larger rotary lobe pumps can also be significantly more expensive than a centrifugal pump of equal flow and head The rotors can be fabricated from metal or rubber, with aluminum rotors being often desirable. Examples of rotary lobe pumps are shown in U.S. Pat. No. 4,940,394 and U.S. Pat. No. 5,567,140.
Rotary lobe pumps do not appear to have been used to pump viscous adhesive resins from storage containers, such a cylindrical drums, to a mixing zone or gun where the resin is mixed with a catalyst. Rotary lobe pumps also do not appear to have been used as metering pumps that mix a resin with a catalyst in a prescribed ratio, such as 10:1, suitable for reaction between the resin and catalyst. Highly viscous, heavy duty adhesives, based on methacrylate resins are widely and increasingly used, primarily in industrial applications. Commonly these viscous resins are dispensed directly from a storage or shipping container, such as a cylindrical 5 or 55 gallon drum. The resin is pumped to a metering pump where it is combined with a suitable catalyst, which tends to be less viscous, and the mixture is dispensed, normally by a mixing or dispensing gun as a bead or in a pattern suitable for a particular application. These viscous resins are difficult to pump. Prior art dispensing units typically employ a ram and a positive displacement piston pump to pump the methacrylate or other viscous resin to a second metering pump. A third pump is used to deliver the catalyst to the metering pump where the two constituent materials are joined in the proper reactive ratio.
Conventional resin dispensing units typically employ a single post ram for use with 5-gallon drums, and a two post ram for use with a 55-gallon drum A drum is secured to the ram. Typically in a two post ram, two air cylinders are joined to tie rods, which are in turn joined to a cylindrical follower plate that is inserted into the drum. A gasket or seal around the periphery of the follower plate engages the inner surface of the drum and the follower plate it forced into the drum to apply pressure on the viscous fluid in the drum. The fluid is then forced upward through an intake opening in the follower plate to a pump, such as a positive displacement piston pump, which then feeds the viscous resin through a hose to the separate metering pump. These dispensing units thus employ at least three separate conventional pumps, which are needed for use with these highly viscous, heavy-duty adhesives and resins. The dispensing units also tend to be quite expensive, which tends to limit the applications in which high performance adhesives, such a highly viscous methacrylate based adhesives, can be used. Dispensing units of this type are also used in other applications. An example of a dispensing unit of this general type is shown in U.S. Pat. No. 4,632,281. FIG. 8 shows a extrusion pump system that employs some of the basic components with which this invention is to be employed. FIG. 8 shows a two post ram 70 attached to tie rods 72 that would be in turn attached to a follower plate, not shown, inside a storage drum 80. This prior art ram applies pressure to the fluid in the drum, but a ram mounted pump 74 is needed to pump fluid from the container to an extrusion gun 76 or another application zone or device.
Unlike the prior art, the invention presented herein eliminates the need for a separate metering pump and resin pump and also employs a rotary lobe configuration in the metering pump to take advantage of the ability of rotary lobe pumps to handle highly viscous fluids.
The preferred embodiment of this invention comprises a 10:1 fixed ratio positive diaplacement metering pump for adhesive or silicone or similar applications. The ratio can be changed simply by replacing a secondary pump with a different mass flow rate. In the preferred embodiment of this invention, a dual rotary, three lobe pump is driven by a centrally located gearbox. The primary lobe pump is force fed on the adhesive or primary fluid side by mounting the pump on a pressure primer ram that applies a downward force on the fluid in a 5 or 55 gallon container. Applications for an apparatus of this type include 10:1 ratio construction adhesives, such as the methacrylate or polyester families and silicone rubbers or other 10:1 ratio material. The gearbox is driven by a C face motor that is typically pneumatically driven or can be driven by a variable speed DC, C face motor.
The pump""s construction utilizes two open-ended pump cavities accessible from each end to replace both rotors and material seals. The gearbox is centrally located and sealed at both ends. The pump assemblies can be removed completely from each end and still leave the gearbox intact.
Current technology requires a ram mounted pump to feed the metering pump. The instant invention provides a single compact, all-in-one metering pump package that is mounted directly to the ram to create a much simpler, lower cost dispensing system. Such a system can also be used to feed a lower pressure sprayer.
According to this invention a metering pump used to pump a first relatively viscous fluid and a second fluid to a mixing zone includes a rotary lobe pump, which transports the first relatively viscous fluid at a first mass flow rate to the mixing zone. An auxiliary rotary pump transports the second fluid at a fixed ratio, relative to the mass flow rate of the first relatively viscous fluid, to the mixing zone so that the two fluids enter the mixing zone to react in a proper ratio. Drive means, which can be a common gearbox, drives the rotary lobe pump and the auxiliary rotary pump.